High-frequency coupling unit



June 24, 1930. KQLSTER 1,766,039

HIGH FREQUENCY COUPLING UNIT Filed May 5, 1926 W 1 U1 [73M IN VENTOR fi'eaer/c/r A. Ao/sferr 61's A rTomvE vs atented June 2% ll3 FREDERICK A. KOLSTER, OF PALO ALTO, CALIFORNIA, ASSIGNOR T FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF GALI- FORNIA.

' HIGH-FREQUENCY COUPLING- UNIT Application filed May 5, 1926. Serial no. 106,827.

This invention relates generally to de vices for coupling together high frequency electrical circuits and which may be incorporated in a radio frequency amplifier system.

In cascade radio frequency amplifiers it is common practice to couple together the various electron emission tubes by means of inductive transformers. Unless elaborate shielding is employed these transformers are apt to have sufficient magnetic linkage between their fields to cause feed back efiects resulting in the generation of local oscillations by the amplifiers.v Such local oscillations cause distortion of the signals and decrease the efiiciency of the system.

It is an object of this invention to devise a coupling device which will have a concentrated magnetic field whereby interlinlrage between successive stages of a vacuum tube amlplifier may be minimized.

t is a further object of this invention to devise a coupling device for a systemwhich will have substantially a constant energy transfer ratio for difierent frequencies within a given range.

It is a further object of this invention to devise a coupling unit especially adapted for use in the system disclosed in my prior application No. 96,290, filed March 23, 1926.

It is a further object of this invention to devise a coupling inductance embodying novel structural details which have high elec trical efliciency and will be cheap to manufacture.

Further objects of the invention will appear from the following description in which I have setforth the preferred embodiment of my invention. It is to be understood that the scope of the invention is to'be determined by the appended claims and the state of the prior art.

Referring to the drawings:

Figure 1 is a side elevational View of the complete coupling unit.

Fig. 2 is a cross section taken along the line 2--2 of Fig. 1.

Fig. 3 is a cross sectional view taken along the line 3--3 of Fig. 1.

Fig. i is a bottom view of the base structure.

Fig. 5 is a transverse vertical sectional view showing the construction of the condenser which is disposed upon the base.

Fig. 6 is a detail view showing diagrammatically the construction of the coil forms.

Fig. 7 is a wiring diagram showing the system with which the coupling unit isadapted to be incorporated.

The device comprises generally a pair of coil forms 10 and 11 which are constructed of some suitable insulating material such as a phenolic condensate product. These forms are substantially semi-cylindrical in shape, that is, each form is D-shaped in cross sectional area as shownin Fig. 2, so that when the two forms are positioned with their flat sides in spaced parallel relationship they will form substantially a cylindrical tances, a secondary inductance S, a relatively small primary inductance L and a second primary inductance L The inductance S is preferably divided equally between the two forms 10 and 11 and therefore comprises apair of oppositely wound coils 13 and 14 which occupy the major portion of the forms 10 and 11. The inductance L may be a'single Ushaped coil wound in close inductive relationship to one of the coils 13 and 14. In the arrangement illustrated it comprises a single coil 15 wound on top of an insulating strip 16 which is wrapped around the lower portion of the coil 13. The inductance L is preferably wound in two D-shaped coils disposed near one end of the forms 10 and 11. Thus as shown in Fig. 6 the lower portions of the forms 10 and 11 may be wound with the two series connected coils 1'! and 18 to form the inductance L The curved cylindrical surfaces of the forms 10 and 11 are threaded to receive the wire of coils l3 and 14, every third turn of each coil being wound between the two preceding turns in order to secure a compact inductance.

Before proceeding further with the structural details of the device the general system with which it is adapted to be incorporated will be described. Such a system has been body. Upon these forms are wound three inducillustrated in Fig. 7 and comprises a plurality of amplifier devices such as electron emission tubes 20 and 21. These tubes may be of the three-element type comprising a grid or control electrode 22, filament or electron emission element 23 and plate or anode 24. The input circuits 25 and 26 respectively of each tube are connected across the grid 22 and filament 23 of each respective tube as is customary practice. Similarly the output circuits 27 and 28 are each connected across a plate 24 and filament 23 and are energized from some suitable source of current such as B batteries 29. The input circuit 25 of the first tube is suitably coupled to a sour'ce of signal energy at radio frequency such as an antenna 31 and ground 32, an antenna inductance 33 beinginduetively coupled with a secondary inductance 34. The output circuit 28 may supply energy to any form of trans? lator T.

For coupling together the output circuit 27 with the input circuit 26 in order to effect a transfer of energy, the output circuit 27 is completed through a plurality of branch impedances 1 and 2, the impedance branch 1 includes the capacitance or condenser C and the inductance L, the condenser and inductance being connected in series. The branch 2 is shunted across the impedance branch 1 and includes a resistance R in series with the inductance L The inductance S is included in the input circuit 26. The system may be selectively tuned throughout a substantial range of radio frequency by means of variable condensers 36 and 37.

Because of the peculiar physical relationship between the various inductances the inductance L is coupled relatively close to the inductance S while the inductance L is coupled relatively loosely to the inductance S. In order to decrease the distributive capacitance between adjacent portions of the coils 13 and 14 these coils are connected in parallel so that the high potential end of each coil 13 and 14 is at its upper end, or at the end which is connected to the grid of the input circuit 26.

The operation of this system has been described in detail in my copending application No. 96,690, filed March 23, 1926. In general however the values of the inductances L and L and that of the capacitance C is so selected that the reactance of the branch 1 v will always be negative throughout the frequency range for which the system is adapted to be used and will decrease negatively with an increase in frequency. The natural period of the branch 2 is selected so as to be outside the frequency range, and its reactance is such that it is positive throughout the frequency range and increases with the frequency. The combined reactance of branches 1 and 2 in'parallel is made negative throughout the frequency range while the reactance of branches 1 and 2 in series is positive throughout the range. Since the resonance frequency of the branches 1 and 2 combined lies just beyond the longest wave length range, the circulatory current flowing between the branches 1 and 2 will be at a minimum when the system is tuned to low wave length but will increase to a maximum value for the longer wave lengths. Thus the lowering of the reactance of inductances L and S due to a decrease in frequency is olfsetby an increase in circulatory current so that the current transfer ratio for the system will tend to remain constant.

Thecoils 17 and 18 are preferably connected in series and have their currents so directed that for circulatory currents they will produce a magnetic field tending to increase the induced current in inductance S and to add to the effect of the inductance L However, for short Wave lengths where circulatory current is at a minimum transfer of energy will be effected by output current in the circuit 27 which splits and flows partly through the branch 1 and partly through the branch 2, thus causing the magnetic field set up by inductance L to oppose the field of inductance L In other words, except for circulatory current, theinductance L is practically in non-inductive relation to the inductance S, this being true because of the dividing up of the inductances L and S into two separate coils each. The resistance R merely serves to increase the decrement of the output circuit 27 in order to make the amplification ratio more nearly constant for the system. The resistance R is inserted in series with the grid of tube 21; that is, between the grid and the oscillatory circuit formed by the secondary S and variable condenser 37. This resistance prevents local oscillations by decreasing the coupling between the input and output circuits afforded by the capacitance between the /'grid and plate of the tube. A similar resistance R has been shown as inserted in series with the grid of the tube 20. From the above it will be understood that the inductances L L and S, and the resistances R R and the capacitance C are all a part of a coupling unit for coupling together two high frequency circuits.

To return to the structural details of the device, the coil forms 10 and 11 are mounted upon a suitable base 40 which is preferably provided with a suitable upstanding flange 41 upon its upper face. The lower ends of the forms 10 and 11 are received within a recess 42 provided upon the flange 41 whereby their inner flat sides are retained in close spaced relationship. The upper ends of these forms are connected together by means of a plate or disc 43 which is clamped to the ends of the forms 10 and 11 by suitable means such as screws 44. The condenser C is disposed within the space surrounded by the flange 41. This contabs 46 extending from one side thereof. The

discs 45 are interleaved by a plurality of similar discs 47 provided with tabs 48 and which are separated from the discs 45 by means of circular washers 49 of mica or other suit able insulating material. The washers and discs are apertured to receive a screw 50 which threads into a presser plate 51 whereby the assembled condenser may be placed under any pressure desired to vary the capacitance between certain limits. To aid in assembling this condenser the tabs 46 and 48 are apertured to receive integral projections 53 extending upward from the base 40. Other integral projections 54 may be provided for positioning the apertured guide tabs 55 and 56 of the discs 45 and 47 respectively. The.

presser plate 51 may also be provided with apertures 57 to receive two of the projections 53 and 54. The conductor tabs 48 and 46 are extended out through slots 59 in the flange 41 to the terminal connections 60 and 61. The bottom face ofthe base is also provided with a recess 63 to receive the two resistances R and R These resistances are constructed similarly, the resistance R comprising for example an insulating'strip 64 wound with a coil of resistance wire 66. A second.

insulating strip 67 overlies the strip 64, the, two strips 65 and 67 being clamped together and to the bottom face of the base 40 by means of screws 68. In the particular instance the screws 68 also extend up into the lower end of the forms 10 and 11, serving to clamp the same to the base. In order to conveniently make electrical connection to the coupling unit the base is provided with other terminal.

connectors 69, 70, 71 and 72. The manner in which the connector terminals are connected windings adapted to be tuned in resonance with radio frequency energy, a relatively small primary coil divided into two portions each portionthereof being closely coupled to one of the pair of windings constituting said secondary coil, and a second primary coil connected with said aforementioned primary windings and loosely coupled to said secondary coil.

2. In a'high frequency coupling unit, a

coil closely coupled to one of said secondary coils, and another primary coil coupled to both of said secondary coils.

3. In a high frequency coupling unit, a secondary inductance coil, a primary inductance coil placed in close inductive relation to said secondary coil and a second primary inductance coil loosely coupled to said secondary coil, the field of said first primary coil being opposed to the field of said second primary coil for current passing through said coils in parallel.

'4. In a high frequency coupling device, a pair of secondary coils of D-shaped cross section positioned with their fiat sides in close parallel relation, a D-shaped primary coil closely coupled to one ofsaid secondary coils, and another pair of coils to form a second primary inductance, said latter pair being D-shaped in cross section and loosely coupled to said pair of secondary coils.

In testimony whereof, have hereto set my 

